Periodic Reporting for period 1 - TWISMA (Twinning with ISMA to develop innovative calorimeters for high energy physics based upon advanced scintillation materials)
Berichtszeitraum: 2023-01-01 bis 2025-12-31
TWISMA’s overall aim is to boost the scientific excellence and innovation capacity of the Institute for Scintillation Materials (ISMA) and its high-quality Twinning partners - European Organization for Nuclear Research (CERN) and Institute of Light and Matter (ILM) – to develop innovative calorimeters for high energy physics (HEP) based upon advanced scintillation materials.
Calorimeters are key components of detectors - used in high-energy experiments for the precise energy measurement of particles - which can be distinguished between two types: homogeneous calorimeters and sampling calorimeters. Homogeneous calorimeters consist of a single dense material, simultaneously acting as an absorber and active material, while sampling calorimeters contain a passive absorber material and an active material for signal generation. Homogeneous calorimeters have a better performance in terms of energy resolution but require bulk volumes of dense scintillation materials, such as scintillating crystals. Meanwhile, sampling calorimeters can be built with a small quantity of active scintillator materials - such as scintillating fibres - but at the expense of reduced energy resolution. Thus, choosing between a homogeneous calorimeter and a sampling calorimeter involves making a trade-off between performance and cost.
For homogenous calorimeters, scintillating inorganic crystals are widely used and have shown excellent performance in several experiments. A prominent example is the electromagnetic calorimeter used in the CMS experiment at the large hadron collider (LHC), which is made of lead tungstate crystals. This calorimeter was instrumental to the discovery of the Higgs bosons in 2012. On the other hand, sampling calorimeters can use plastic scintillators, as their density is not critical for the absorption power. However, the radiation tolerance of inorganic crystals is usually superior to that of plastic scintillators.
The high luminosity LHC foreseen for 2028 – as well as new collider projects currently under study (e.g. high intensity electron-positron collider, extreme energy proton-proton collider and muon collider) - will require detectors capable of withstanding very high collision rates. Such detectors will need to demonstrate excellent energy and position resolution, as well as high radiation tolerance and precise timing resolution well beyond the current state-of-the-art. Besides their use in calorimeters for high energy physics, scintillation materials are also found in many other applications such as radiation detectors and positron emission tomography (PET).
Within TWISMA’s preparatory research project, the Twinning partners are focused on developing advanced scintillation materials for homogeneous and sampling calorimeters. Namely, they investigate ways to improve the scintillation properties of two types of advanced inorganic scintillating crystal - Ce-doped garnets and bismuth germanate-silicate oxides (Bi4Ge3-xSixO12) - by optimising the crystal growth production processes to achieve the state-of-the-art performance characteristics.
Calorimeters are key components of detectors - used in high-energy experiments for the precise energy measurement of particles - which can be distinguished between two types: homogeneous calorimeters and sampling calorimeters. Homogeneous calorimeters consist of a single dense material, simultaneously acting as an absorber and active material, while sampling calorimeters contain a passive absorber material and an active material for signal generation. Homogeneous calorimeters have a better performance in terms of energy resolution but require bulk volumes of dense scintillation materials, such as scintillating crystals. Meanwhile, sampling calorimeters can be built with a small quantity of active scintillator materials - such as scintillating fibres - but at the expense of reduced energy resolution. Thus, choosing between a homogeneous calorimeter and a sampling calorimeter involves making a trade-off between performance and cost.
For homogenous calorimeters, scintillating inorganic crystals are widely used and have shown excellent performance in several experiments. A prominent example is the electromagnetic calorimeter used in the CMS experiment at the large hadron collider (LHC), which is made of lead tungstate crystals. This calorimeter was instrumental to the discovery of the Higgs bosons in 2012. On the other hand, sampling calorimeters can use plastic scintillators, as their density is not critical for the absorption power. However, the radiation tolerance of inorganic crystals is usually superior to that of plastic scintillators.
The high luminosity LHC foreseen for 2028 – as well as new collider projects currently under study (e.g. high intensity electron-positron collider, extreme energy proton-proton collider and muon collider) - will require detectors capable of withstanding very high collision rates. Such detectors will need to demonstrate excellent energy and position resolution, as well as high radiation tolerance and precise timing resolution well beyond the current state-of-the-art. Besides their use in calorimeters for high energy physics, scintillation materials are also found in many other applications such as radiation detectors and positron emission tomography (PET).
Within TWISMA’s preparatory research project, the Twinning partners are focused on developing advanced scintillation materials for homogeneous and sampling calorimeters. Namely, they investigate ways to improve the scintillation properties of two types of advanced inorganic scintillating crystal - Ce-doped garnets and bismuth germanate-silicate oxides (Bi4Ge3-xSixO12) - by optimising the crystal growth production processes to achieve the state-of-the-art performance characteristics.
• Two simultaneous lines of research in development of garnet scintillators have been developed in the project. ISMA has optimized composition and crystal growth conditions by the Czochralski method of YAG:Ce crystals codoped with divalent codopants, while ILM group developed GAGG:Ce-based scintillators with the same dopants growth by the micro-pulling-down method. Both crystals were optimized by the feedback from CERN.
• The obtained results certify that scintillation parameters of Ce-doped YAG and GAGG are improved at certain combination of Ca and Mg codopants, which eliminates carrier traps and accelerates carrier transport to luminescence centres independently on the host composition.
• Apart of that, YAG is more promising as host, because it can be obtained in cheap W/Mo crucibles in contrast to GAGG and other Ga-containing crystals. Moreover, it does not contain Gd ions, which may call slow components in scintillation decay due to energy transport via Gd3+ sublattice. Moreover, Gd is a heavy atom, which may be subjected to radiation damage by charged hadrons in high energy physics experiments.
• Due to the synergy between Ca2+ and Mg2+ doping of garnets hosts, we demonstrated that improved combination of light yield and decay time can be achieved in Ce-doped garnets, i.e. larger number of prompt photons can be generated for fast-timing applications.
• Addition of dopants (Ta, Gd, Al) has not improved scintillation parameters but worsened crystallization conditions, resulting in larger quantity of inclusions in BSO/BGSO crystals.
• Transfer to BGSO solid solutions, although provided congruent melting and growth by the Czochralski method, did not enhance crystal quality because of cracks generated by SiO2 inclusions called by bismuth dioxide evaporation, and large difference in ionic radii between substitutional Si4+/Ge4+ cations creating mechanical stress in crystals.
• Coincidence timing resolution (CTR) of undoped BSO was improved to 125 ps by tuning growth atmosphere composition that provides minimization of SiO2 evaporation and reducing amount of Pt dissolving into the melt and, consequently, decreases the number of inclusions in crystals. As BSO is crystallized from Bi2O3-enriched melt-solution, further optimization of growth conditions is necessary to get large-size crystals with acceptable optical quality and enhanced radiation hardness.
• The decay time of GAGG:Ce,Mg fiber-shaped crystals decreased with Mg content to 0.5-2 ns, whereas light yield was below 2000 ph/MeV; the parameters were stable along the fibers grown by the micro-pulling-down method. Further tuning of Mg and Ca dopant content is necessary to determine optimal composition to grow large GAGG-based crystals by the Czochralski method.
• In the framework of R&D for the upgrade of the electromagnetic calorimeter of LHCb upgrade a cojoined work between CERN EPR&D and PICOcal group from LHCb collaboration development of W absorber made by 3D printing has been pursued. First prototype consisting of three blocks of 121.2x121.2x50 mm3 have been produced with 8x8x81 holes of 1.2x1.2mm2 for insertion of crystal fibres.
• The obtained results certify that scintillation parameters of Ce-doped YAG and GAGG are improved at certain combination of Ca and Mg codopants, which eliminates carrier traps and accelerates carrier transport to luminescence centres independently on the host composition.
• Apart of that, YAG is more promising as host, because it can be obtained in cheap W/Mo crucibles in contrast to GAGG and other Ga-containing crystals. Moreover, it does not contain Gd ions, which may call slow components in scintillation decay due to energy transport via Gd3+ sublattice. Moreover, Gd is a heavy atom, which may be subjected to radiation damage by charged hadrons in high energy physics experiments.
• Due to the synergy between Ca2+ and Mg2+ doping of garnets hosts, we demonstrated that improved combination of light yield and decay time can be achieved in Ce-doped garnets, i.e. larger number of prompt photons can be generated for fast-timing applications.
• Addition of dopants (Ta, Gd, Al) has not improved scintillation parameters but worsened crystallization conditions, resulting in larger quantity of inclusions in BSO/BGSO crystals.
• Transfer to BGSO solid solutions, although provided congruent melting and growth by the Czochralski method, did not enhance crystal quality because of cracks generated by SiO2 inclusions called by bismuth dioxide evaporation, and large difference in ionic radii between substitutional Si4+/Ge4+ cations creating mechanical stress in crystals.
• Coincidence timing resolution (CTR) of undoped BSO was improved to 125 ps by tuning growth atmosphere composition that provides minimization of SiO2 evaporation and reducing amount of Pt dissolving into the melt and, consequently, decreases the number of inclusions in crystals. As BSO is crystallized from Bi2O3-enriched melt-solution, further optimization of growth conditions is necessary to get large-size crystals with acceptable optical quality and enhanced radiation hardness.
• The decay time of GAGG:Ce,Mg fiber-shaped crystals decreased with Mg content to 0.5-2 ns, whereas light yield was below 2000 ph/MeV; the parameters were stable along the fibers grown by the micro-pulling-down method. Further tuning of Mg and Ca dopant content is necessary to determine optimal composition to grow large GAGG-based crystals by the Czochralski method.
• In the framework of R&D for the upgrade of the electromagnetic calorimeter of LHCb upgrade a cojoined work between CERN EPR&D and PICOcal group from LHCb collaboration development of W absorber made by 3D printing has been pursued. First prototype consisting of three blocks of 121.2x121.2x50 mm3 have been produced with 8x8x81 holes of 1.2x1.2mm2 for insertion of crystal fibres.
Fabrication of a sampling calorimeter requires large number of fibre-shaped crystals with the optimized composition embedded into a metal absorber. For final detector for the inner part of LHCb upgraded calorimeter a total of 40 modules each containing 5184 fibres of 1.x1x50mm3 and 1x1x100mm3 fibres will be needed. A first W absorber for one module is under production and will be used to test the performance in terms of timing of light output of the YAG and GAGG fibres with optimal composition produced at ILM and ISMA under high energy particles beam at the end of the year 2024 or during 2025.
Concerning the concept of dual readout calorimeter, simulation framework using Geant4 simulation tool are currently under development to identify the best way to discriminate scintillation and Cherenkov emission from pulse shape. First test under high energy beam will be performed with a PWO crystal in summer 2024 to assess the method, similar tests will be performed with BSO samples with sufficient size will be grown at ISMA.
Concerning the concept of dual readout calorimeter, simulation framework using Geant4 simulation tool are currently under development to identify the best way to discriminate scintillation and Cherenkov emission from pulse shape. First test under high energy beam will be performed with a PWO crystal in summer 2024 to assess the method, similar tests will be performed with BSO samples with sufficient size will be grown at ISMA.